Currently, there is an increasing interest in truly biodegradable polymers. Biodegradable polymers have been used in medical and pharmaceutical applications for a number of years in applications such as absorbable sutures and controlled release of clinical drugs. There have been some attempts to use such polymers in commodity polymer applications such as packaging, film wrap and food applications. Unfortunately, many of these types of polymers have a relatively low glass transition temperature (or Tg) and a relatively low heat distortion temperature. Such a low heat distortion temperature makes the polymers per se unsuitable for use in applications where the polymer will be exposed to moderate to high temperatures such as the boiling temperature of water (e.g. hot drink containers such as coffee and tea cups and microwave containers).
There are several types of biodegradable polymers which may be competing in the same application fields or they may be complementary. The polylactides or homopolymers of lactic acid are one type of degradable polymer. Polyhydroxy alkanoates (PHA) are another type of biodegradable polymer. The polyhydroxy alkanoates may be represented by homopolymers of 3-hydroxy butyrate (sometimes also referred to as PHB) or copolymers with 3- or 4-hydroxy valerate (sometimes called PHBV).
PCT Patent Application WO 90/01521 filed Aug. 4, 1989 in the name of Battelle Memorial Institute contains a good description of the prior art in the field of homopolymers of lactic acid. The patent application discusses a number of applications of polylactic acid. In the disclosure of the third general embodiment beginning at page 65 of the patent application, there is a discussion of various blends of polylactic acid with other polymers. The other polymers include polystyrene, polyethylene, polyethylene terephthalate and polypropylene. In the disclosure of WO 90/01521 at page 74, there is an additional list of monomers which may be polymerized to form polymers which may be blended with polylactic acid. The monomers include styrene, ethylene, propylene, vinyl chloride, vinyl acetate, alkyl methacrylates, alkyl acrylates and physical mixtures thereof.
The patent application does not address the issue of the Tg of polylactic acid. Furthermore, the patent application does not suggest alloys of polylactic acid with polycarbonate, imidized acrylates and polymers containing anhydrides of ethylenically unsaturated dicarboxylic acids. Additionally, the patent application does not contemplate all of the copolymeric biodegradable polymers of the present invention.
U.S. Pat. No. 4,477,654 issued Oct. 16, 1984, assigned to Imperial Chemical Industries PLC discloses copolymers of various hydroxy alkanoates. The patent, however, does not contemplate the formation of alloys of such polymers with the polymers of the present invention.
U.S. Pat. No. 4,246,374 issued Jan. 20, 1981, assigned to Rohm and Hass Company discloses the imidized type of polymers which may be used in the present invention. However, the patent does not disclose or suggest that such polymers could be alloyed or blended with the biodegradable polymers of the present invention.
Polymers of a vinyl aromatic compound such as styrene and anhydrides of ethylenically unsaturated dicarboxylic acids which may optionally contain (meth)acrylic esters have been known as illustrated by U.S. Pat. No. 3,336,267 now expired and U.S. Pat. No. 4,569,969 issued Feb. 11, 1986, assigned to Monsanto. Investigations relating to the use of such polymers in blends have continued as represented by U.S. Pat. No. 4,631,311 issued Dec. 23, 1986, assigned to BASF. However, none of the art located by the applicants discloses or suggests blending such polymers with biodegradable polymers of the type of the present invention.
There is a need to provide an alloy comprising a biodegradable polymer which has a higher Tg, heat distortion temperature and/or a higher melting temperature. The present invention seeks to provide such a polymer alloy or blend.